In green mode, for example, pulse skipping mode, diode emulated mode, etc, a switching regulator will detect zero current for disabling the low-side power switch to prevent from reverse inductor current that may cause extra efficiency loss. Traditionally, the zero current detection is implemented by comparing the voltage of the switching node with some threshold such as ground potential, for example, disclosed by U.S. Pat. No. 7,327,127. However, the threshold for identifying a zero current is fixed in the circuit design and thus, when some component has different characteristics, for example, the comparator offset and delay time, the resistance of the high-side or low-side power switch, and the noise effect at the switching node, the low-side power switch may be turned off too early or too late, and consequently it can't precise to optimize the efficiency in green mode.